Engineered material arresting system and methods for forming same

ABSTRACT

A method of forming a vehicle arresting system includes installing a plurality of stratified layers of aggregate and compressing each layer prior to adding a next aggregate layer, a slab layer, and/or some other separation layer. In one aspect, one or more of the aggregate layers comprises a glass foam, and one or more of the slab layers comprises a cementitious material having an oven-dry density of 100 lb/ft3 or less, such as cellular concrete. The aggregate layers may be poured to approximately the same depth as one another, or at least one aggregate layer may have a different depth than the other aggregate layers. Similarly, the method of compaction for one aggregate layer may be the same as or different from the method used for the other aggregate layers.

This application is a continuation of U.S. patent application Ser. No.15/912,422, filed Mar. 5, 2018, which claims the benefit of priority toU.S. Provisional Patent Application No. 62/466,922, filed Mar. 3, 2017,the contents of both which are incorporated herein by reference in theirentirety.

BACKGROUND 1. Field of the Invention

The present application relates to a system for arresting aircraft thathave overrun a runway end and methods for constructing such a system.

2. Description of the Related Art

Airport runways are configured to accommodate the takeoff and landing ofmultiple types of aircraft. While the overwhelming number of thoseevents occur without incident, there may be times when an aircraftoverruns its runway and needs to be arrested. One such method forarresting aircraft is to position an engineered material arrestingsystem (EMAS) in the safety area past the end of the runway. The EMASincludes an energy dissipating, deformable, crushable, and/orcompactible material that engages the aircraft wheels and slows theaircraft by dissipating its kinetic energy. The material in the EMAS isdesigned to compact and give way to the aircraft tires during an overrunevent.

EMAS installations may be located at one or both ends of a runway. TheEMAS may be subjected to jet blast loads from aircraft taking off awayfrom the EMAS or taxiing past the EMAS. Those loads typically generateupward lift on the EMAS, which may result in damage to an uncovered bedof material. As a result, the integrity of the EMAS may be at leastpartially compromised, debris may be spread across the runway area, andthe effectiveness of the EMAS may be reduced.

One method for countering the uplift forces has been to embed continuousgeogrid walls within the bed of compactible material, the walls placedin the overrun direction of the bed. The geogrid is a mesh-likestructure that attaches to the underlying pavement using one or moreanchors along its length. The geogrid may protrude above the compactiblematerial when that material is first placed, which makes grading thematerial more difficult, and slows down the installation process.Moreover, in the event of damage to the geogrid, repair efforts mayrequire excavating large portions of the compactible material in orderto replace a length of geogrid.

During overrun events, in which an aircraft leaves the runway and isarrested by the EMAS system, it has been observed that arresting loadson the aircraft can increase at higher aircraft exit speeds. Thus, someaircraft for some EMAS systems may have maximum exit speeds that arelimited by landing gear loading rather than available EMAS length.

It has been observed that smaller, lightweight aircraft may lack theweight and tire loading necessary for effective engagement with the EMASduring an overrun event. In those situations, rather than the aircrafttires engaging and/or embedding with the EMAS material, they may rollover the EMAS with little or marginal vertical penetration into thematerial, which can result in reduced effectiveness of that system.

BRIEF SUMMARY

In one aspect, a vehicle arresting system includes a base layercomprising a crushable aggregate and a cover layer comprising acementitious material having an oven-dry density of 100 lb/ft3 or less.In another aspect, a vehicle arresting system includes a base layercomprising a crushable aggregate and a cover layer comprising acementitious material having an oven-dry density between about 40 lb/ft3and about 100 lb/ft3, or between about 40 lb/ft3 and about 90 lb/ft3, orbetween about 40 lb/ft3 and about 80 lb/ft3, or between about 40 lb/ft3and about 70 lb/ft3, or between about 40 lb/ft3 and about 60 lb/ft3, orbetween about 40 lb/ft3 and about 50 lb/ft3.

In another aspect, a vehicle arresting system includes an arrestor bedand a plurality of anchors. Each anchor includes a support rod coupledto an associated puck, each support rod being secured to the safety areapavement underlying the arrestor bed, and each puck being embedded inthe cover layer of the arrestor bed. Additionally, each support rod iscoupled to its associated puck via a shear linkage designed to break ata predetermined load.

In another aspect a method for arresting a vehicle includes depositing abase layer on a region where the vehicle is to be arrested, the baselayer comprising an aggregate, and depositing a cover layer over thebase layer, the cover layer comprising a cementitious composition havingan oven-dry density of 100 lb/ft3 or less.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a section view of an EMAS including a plurality of pointanchors taken perpendicular to a direction of travel;

FIG. 2 is a second section view of an EMAS including a plurality ofpoint anchors taken perpendicular to a direction of travel;

FIG. 3 is a section view of a below-grade basin filled with an EMAS foruse with a plurality of point anchors, the section taken parallel to adirection of travel;

FIG. 4 is a section view of an above-grade embodiment of an EMAS for usewith a plurality of point anchors, the section taken parallel to adirection of travel;

FIG. 5 is an isometric view of a point anchor subassembly for use in anEMAS;

FIG. 6 is a section view of the point anchor subassembly of FIG. 5;

FIG. 7 is a top view of the point anchor subassembly of FIG. 5;

FIG. 8 is a bottom view of the point anchor subassembly of FIG. 5;

FIG. 9 is a side view of the point anchor subassembly of FIG. 5;

FIG. 10 is a section view of another embodiment of a point anchorsubassembly;

FIG. 11 is a top view of the point anchor subassembly of FIG. 10;

FIG. 12 is a series of isometric detail views of a breakaway orfrangible fuse within a point anchor subassembly;

FIG. 13 is a series of isometric detail views of a breakaway orfrangible fuse within a point anchor subassembly depicting failure ofthe fuse along an engineered fracture path;

FIG. 14 is a side view of the point anchor subassembly of FIG. 5 alsodepicting distributed upward loading forces caused by slab uplift loadsfrom aircraft jet blast;

FIG. 15 is one depiction of a top view of an EMAS divided into aplurality of zones having different anchor configurations;

FIG. 16 is a second depiction of a top view of an EMAS divided into aplurality of zones having different anchor configurations;

FIG. 17 is a finite element fringe plot representing deflections withina puck component of a point anchor subassembly is subjected to 1,500pounds of upload force;

FIG. 18 is a finite element fringe plot representing the Von Misesstresses of the puck of FIG. 14 during the same loading;

FIG. 19 is a finite element depiction of an overrun simulation in whichan airplane tire penetrates the EMAS by 6 inches;

FIG. 20 is a finite element depiction of an overrun simulation in whichan airplane tire penetrates the EMAS by 12 inches;

FIG. 21 is a flowchart depicting one method for installing an EMAS;

FIG. 22 is a flowchart depicting a second method for installing an EMAS;

FIG. 23 is a graph of normalized drag force versus distance for oneexample of the present EMAS;

FIG. 24 depicts several examples of actual versus predicted failuremodes of a puck utilized in an EMAS;

FIG. 25 is a bottom view of one view of a slab section utilized in anEMAS;

FIG. 26 is a section view through line A-A in FIG. 25;

FIG. 27 is a bottom view of multiple slab sections having ribbedportions disposed perpendicular to a runway direction;

FIG. 28 is a bottom view of multiple slab sections having ribbedportions disposed parallel to a runway direction;

FIG. 29 is a bottom view of another view of a slab section utilized inan EMAS;

FIG. 30 is a section view through line A-A in FIG. 29;

FIG. 31 is a section view through line B-B in FIG. 29;

FIG. 32 is a bottom view of a slab section having waffle portionsdisposed perpendicular to a runway direction;

FIG. 33 is a bottom view of a slab section having waffle portionsdisposed at an angle to a runway direction;

FIG. 34 is a bottom view of multiple slab sections havingdifferently-sized waffle portions disposed perpendicular to a runwaydirection;

FIG. 35 is a bottom view of multiple slab sections havingdifferently-sized, circular-shaped waffle portions;

FIG. 36 is a section view of an EMAS having a first type of void betweenslab and aggregate layers;

FIG. 37 is a section view of an EMAS having a second type of voidbetween slab and aggregate layers;

FIG. 38 is a section view of an EMAS having a third type of void betweenslab and aggregate layers;

FIG. 39 is a top view of an EMAS with geogrid being used to secure theslab to an underlying pavement;

FIG. 40 is a section view through line A-A in FIG. 39;

FIG. 41 is a top view of an EMAS with point anchors being used to securethe slab to an underlying pavement;

FIG. 42 is a section view through line A-A in FIG. 41;

FIG. 43 is a section view of an EMAS taken perpendicular to a runwaydirection illustrating an aircraft tire punching through a slab layer ata location above a void;

FIG. 44 is a section view of an EMAS taken parallel to a runwaydirection illustrating displacement of aggregate into a void between theaggregate and slab during an overrun event;

FIG. 45 is a sequence of top views of abutting aggregate portions usedto form the aggregate layer of an EMAS;

FIG. 46 is a section view through line A-A in FIG. 45;

FIG. 47 is a sequence of top views of a first instance of overlappingaggregate portions used to form the aggregate layer of an EMAS;

FIG. 48 is a section view through line A-A in FIG. 47;

FIG. 49 is a sequence of top views of a second instance of overlappingaggregate portions used to form the aggregate layer of an EMAS;

FIG. 50 is a section view through line A-A in FIG. 49;

FIG. 51 is a section view of an EMAS, illustrating a first method ofinstalling geogrid to the pavement using an adhesive;

FIG. 52 is an isometric view of the pavement and geogrid of FIG. 51;

FIG. 53 is a detail view of the adhesive connection of FIG. 51;

FIG. 54 is an isometric view of a second method of installing geogrid tothe pavement using an adhesive;

FIG. 55 is a detail view of the adhesive connection of FIG. 54;

FIG. 56 is an isometric view of a third method of installing geogrid tothe pavement using an adhesive;

FIG. 57 is a detail view of the adhesive connection of FIG. 56;

FIG. 58 is an isometric view of a fourth method of installing geogrid tothe pavement using an adhesive;

FIG. 59 is a detail view of the adhesive connection of FIG. 58;

FIG. 60 is an isometric view of a fifth method of installing geogrid tothe pavement using an adhesive;

FIG. 61 is a detail view of the adhesive connection of FIG. 60;

FIG. 62 is a section view of one aspect of an EMAS depicting multipleaggregate layers;

FIG. 63 is a section view of a second aspect of an EMAS depictingmultiple aggregate layers;

FIG. 64 is a section view of a third aspect of an EMAS depictingmultiple aggregate layers;

FIG. 65 is a section view of a fourth aspect of an EMAS depictingmultiple aggregate layers;

FIG. 66 is a section view of a fifth aspect of an EMAS depictingmultiple aggregate layers;

FIG. 67 is a section view of a large aircraft tire rolling through theEMAS of FIG. 62;

FIG. 68 is a section view of a smaller aircraft tire rolling through theEMAS of FIG. 62;

FIG. 69 is a section view of an EMAS incorporating a lid;

FIG. 70 is a bottom view of on type of lid used in the EMAS of FIG. 69;

FIG. 71 is a bottom view of a second type of lid used in the EMASS ofFIG. 69;

FIG. 72 is a detail view of the interface between lid stiffening agentsand a support sheet;

FIG. 73 is a detail view of the interface between lid stiffening agentsand support props;

FIG. 74 is a depiction of one type of support prop;

FIG. 75 is a depiction of a second type of support prop;

FIG. 76 is a depiction of a third type of support prop;

FIG. 77 is a depiction of a fourth type of support prop; and

FIG. 78 is a section view of an EMAS with a lid, depicting anchoring ofthe lid to the underlying pavement.

DETAILED DESCRIPTION

In one aspect, as seen in FIGS. 1-4, an engineered material arrestingsystem (EMAS) 50 includes an arrestor bed 52 comprising a basin filledwith an aggregate 54, a slab 56 disposed on top of the aggregate 54, anda topcoat 58. The arrestor bed 52 may be a basin that includes portionsbelow-grade of the runway, as seen in FIG. 3. In another aspect,however, some or all of the EMAS may be at or above runway grade, asbest seen in FIG. 4. For example, a bottom of the basin may be at runwaygrade, and there may be an incline, a mound, a ramp, or some similarstructure extending above ground to a top of the basin.

Multiple materials may be used for each layer in the EMAS 50, as will bediscussed in greater detail below. However, in one aspect, the aggregate54 may be a glass foam aggregate such as the material available underthe trade name Glasopor. The slab 56 may be a controlled low-strengthmaterial (CLSM) or a cellular concrete material. The topcoat 58 may be ahigh friction surface treatment such as methyl methacrylate (MMA) soldunder the trademark TRANSPO T-18 or T-28. Alternatively, the topcoat 58may comprise poly-urea, epoxy, or a sprayed- or poured-on finish.

The aggregate 54 may be a crushable, compactable material. For example,the aggregate 54 may be a glass foam fill with average aggregate sizesbetween 1 and 3 inches, and with a range of compaction strengths. In oneaspect, the glass foam may be, e.g., grade 24 or grade 18 Glasopor,which have crush pressures of 24 psi and 18 psi, respectively. In oneaspect, the EMAS bed may use a single aggregate 54 along its length. Inanother aspect, as seen in FIGS. 3 and 4, a first aggregate may fill afirst portion of the bed, and a second, different grade of aggregate mayfill a second portion of the bed. For example, the higher crush-strengthaggregate may fill an entry portion of the bed. Alternatively, a lowercrush-strength aggregate may fill the entry portion of the bed.

The slab 56 may be a low strength material that is configured to failupon loading by an aircraft tire. One such material is CLSM, which is aparticular form of cementitious material that may have a compressivestrength between about 200 and about 600 psi, with a density of about110 to 130 lb/ft³. In one example, CLSM may be made by mixing sand,cement, fly ash, water, admixtures, and fibers. Due to its combinedstrength and density, CLSM may be well-suited to resisting jet blastuplift forces. At the same time, however, its high density may causehigher inertial loading during overrun, which may increase the forcesplaced on the aircraft tires that are then transmitted to the landinggear components. In one aspect, a single slab material may be used alongthe length of the system 50. In another aspect, as seen in FIGS. 3 and4, a first slab material may fill a first portion of the bed, and asecond, different slab material may fill a second portion of the bed. Asthose figures illustrate, the first slab portion may have a differentlongitudinal extent along a length of the EMAS than the first aggregateportion. For example, the first slab portion may extend longitudinally agreater distance than the first aggregate portion. In another aspect,the first slab portion may extend longitudinally a shorter distance thanthe first aggregate portion. In still another aspect, the first slabportion and the first aggregate portion may extend substantially thesame longitudinal distance along the EMAS. Additionally, similarvariations are possible for subsequent slab and aggregate portions.

In another aspect, the slab 56 may be formed from cellular concrete,which is a lightweight, cementitious material that contains stable airor gas cells uniformly distributed throughout the material, e.g., at avolume greater than 20%. As such, cellular concrete may include about65% void space, allowing that material to undergo considerablevolumetric compaction and energy dissipation, e.g., when being overrunby an aircraft tire. Cellular concrete may be formed, e.g., by mixingwater and a foaming agent to generate a preformed foam. That preformedfoam then may be mixed with cement and water. Fibers then may be addedto the mix to help increase crack resistance and tensile straincapacity. Finally, the mixture may be poured and leveled, just likeother cement compositions. The cellular concrete used herein may conformto specifications established by the American Concrete Institute.

Cellular concrete may have a compressive strength of between about 200psi and about 600 psi, i.e., approximately the same strength as CLSM. Atthe same time, cellular concrete may be significantly lighter than CLSM,having a density of between about 40 lb/ft³ and about 50 lb/ft³. As aresult, an EMAS 50 that incorporates cellular concrete within its slab56 may have improved exit speed ratings and improved small-aircraftperformance as compared to an EMAS that includes solely CLSM as its slab56 material. Additionally, the use of cellular concrete may surprisinglyprovide substantially the same compressive strength as other materialssuch as CLSM, but at a fraction of the density, thereby cutting a weightof the slab 56 by a factor, e.g., of between about 3 and about 3.5.

Use of a slab 56 may dramatically alter the effective strength of theaggregate 54 during an overrun event. In particular, the aggregate 54exhibits pressure-dependent shear strength behavior similar to that ofsoil or other geomaterials. By covering that layer, the slab 56 mayconfine and increase the material strength of the aggregate 54 byproviding a dead load that causes mild and constant static overburden,by providing an inertial resistance to vertical aggregate movement andblunting a bow wave of aggregate ahead of a tire during the overrun, andby providing non-inertial resistance to aggregate movement through theflexural strength of the slab. Accordingly, the slab confines movementof the aggregate, increasing hydrostatic pressures and the effectiveshear strength of the aggregate.

The slab 56 also may dissipate energy during an overrun event throughshear failure, as a shear failure line is formed on the inboard andoutboard sides of each tire that cuts through the slab 56. The slab 56also may absorb energy from the tire, as that tire pulls slab materialunderneath it and crushes that material through mixed-mode fracture andfrictional grinding of the pulverized slab material against itself. Theslab 56 also may provide inertial resistance to the aircraft tire andabsorb momentum proportional to aircraft speed and the displaced slabmass.

Returning to FIG. 1, the EMAS 50 additionally may include a plurality ofpoint anchors 60 configured to assist in retaining the rest of the EMAS50 in place when subjected to upward forces generated by jet blastand/or to dissipate airplane energy during an overrun or arrestingevent. A point anchor 60 includes an embedment puck 62 and a strap orrod 64 coupled to the puck 62 at a proximal end 66 and depending, i.e.,extending, downwardly from the puck 62. A pavement anchor 68 secures therod 64 or strap to the pavement underlying the EMAS. For example, a boltor rivet may secure a mounting plate 70 at a distal end 72 of the rod 64to the underlying pavement.

Turning to FIGS. 5-9, the embedment puck 62 includes a hub 74 thatreceives the proximal end 66 of the rod 64 and a cap 76 frangiblycoupled to the hub 74. The cap 76 includes an upper surface 78 that, inone aspect, may be substantially smooth. In another aspect, the uppersurface 78 may include one or more marks 80 to facilitate breaking ofthe cap 76 into multiple pieces or to provide relief for post-moldingcooling of the puck 62, thereby promoting uniform thickness of the cap76. The marks 80 may be arranged in a pattern about the upper surface78. For example, the marks 80 may radiate outward from a central cavity82 of the upper surface 78 and may be substantially equidistantly spacedin order to divide the upper surface 78 into a plurality of wedges 84.The cap 76 may be substantially circular when viewed from above.Alternatively, the cap 76 may take on various other shapes, such as atriangle, rectangle, pentagon, hexagon, etc.

The point anchor 60 also may include a top plug (not shown) that coverssome or all of the cap 76. In particular, the top plug may be configuredto cover at least the central cavity 82 of the cap 76, thereby coveringthe nuts holding the puck 62 in place and preventing cover layer slurry,dirt, water, or other foreign body intrusion into the central cavity 82.The top plug in one aspect may be installed prior to pouring of the slab56 and/or application of the topcoat 58, thereby preventing intrusion ofslab slurry and/or topcoat materials into the central cavity 82.

The cap 76 also may include an underside 86 interrupted by a pluralityof radial stiffeners 88. The stiffeners 88 may be equidistantly spacedaround the puck and may extend radially from the hub 74 to an outerperiphery 90 of the puck 62. Each stiffener 88 may extend downwardlyfrom the underside 86 a greater longitudinal distance proximate the hub74 than the outer periphery 90. For example, each stiffener 88 may beapproximately triangular, with the hypotenuse 92 connecting the outerperiphery 90 to the hub 74. The stiffeners 88 may take on other shapes,including, e.g., having a concave or convex edge replacing thehypotenuse, as would be appreciated by one of ordinary skill in therelevant art.

As seen in FIGS. 5 and 6, one or both of the hub 74 and the centralcavity 82 may include an opening configured to receive the rod 64. Forexample, the rod 64 may include external threading 94, and the hub 74and/or the central cavity 82 may include internal threading.Alternatively, the hub 74 and/or central cavity 82 may be configured toreceive one or more nuts 96, the nuts 96 having threading 98 forengaging the threading 94 on the rod 64. For example, the hub 74 and/orcentral cavity 82 may be molded to have a hexagonal shape or anothershape matching that of the nuts 96 or otherwise preventing rotation ofthe nuts 96 relative to the hub 74 and/or central cavity 82. The systemmay include a pair of nuts 96 a, 96 b disposed within the hub 74,proximate the cap 76 and a third nut 96 c spaced from the first two nuts96 a, 96 b and disposed proximate a bottom of the hub 74. A washer 100may be disposed between the pair of nuts 96 a, 96 b and the third nut 96c, the washer 100 resting on a flange 102 formed within the hub 74. Assuch, the washer 100 and nuts 96 a, 96 b may be inserted into the hub 74from the top, through the central cavity 82, and the nut 96 c may beinserted into the hub 74 from the bottom. The washer 100 may becompressible in order to accommodate thermal expansion and compressionof the point anchor components, including the rod 64.

In another aspect, instead of a threaded connection, the rod 164 mayinclude a plurality of teeth 165, and the puck 162 may include or beoperatively coupled to a ratchet configured to slide along the teeth,similar to a zip tie-type connection, as best seen in FIGS. 10 and 11.In the event the puck 162 is depressed too far, the ratchet may includea release mechanism that disengages the ratchet from the teeth, therebypermitting the puck 162 to be reversed in direction along the rod 164.Such a connection may permit rapid installation of a plurality of pucks162 while also preventing vertically upward displacement of the pucks162 during normal jet blast uplift due to the one-way nature of suchconnectors.

Turning now to FIGS. 12 and 13, and with reference to the puck of FIGS.5-9, the puck 62 further may include an intentional weak link 104, whichmay take the form of a fuse 106 at the center of the puck 62. The fuse106 may be formed within the hub 74 or the central cavity 82 and mayinclude a plurality of shear links or ribs 112 spaced about a peripheryof the fuse 106 and extending longitudinally along at least a portion ofthe length of the fuse 106 for facilitating separation of the rod 64,nuts 96, and washers 100 from the hub 74.

The puck 62 and other elements of the point anchors 60 may be sizedaccording to the loads to which they are expected to be exposed. Forexample, the strength of the slab 56 may drive the sizing of the puck62. In one example, the slab 56 may have a strength of about 200 to 600psi. When accounting for a factor of safety, the cap 76 of the puck 62then may have a diameter between about 4 inches and about 12 inches, orbetween about 4 inches and about 8 inches, and in one aspect, about 6inches. Relatedly, a lower slab strength may require the use of largerpucks 62.

The puck 62 also may have a height between about 1 inch and about 6inches, or between about 1 inch and about 4 inches, and in one aspect,about 2 inches. Between about ¼ inch and 1 inch of that height, orbetween about ½ inch and 1 inch of that height, or in one aspect, about⅝″ of that height may correspond to a portion of the hub 74 free fromstiffeners 88. Moreover, the wedges 84, stiffeners 88, the hub 74 allmay have a substantially different or similar thickness. For example,each of those components may have a thickness of about 1/32 inch to ¼inch, or in one aspect, about 1/16 inch, although other thicknesses forone or more of the components may be possible, e.g., depending on thesize of the remainder of the puck 62, the number of pucks 62 in aninstallation, the design load, etc.

The rod 64, nuts 96, and washer 100 may be selected based on the commonavailability of such components. For example, the rod 64 may have athreaded diameter of about ¼ inch to ½ inch, or in one aspect, about ⅜inch, and the nuts 96 and washer 100 similarly may having internaldiameters of about ¼ inch to ½ inch, or in one aspect, about ⅜ inch. Therod 64 and nuts 96 also may have similar thread counts, e.g., 16 to 24threads per inch, in order to successfully couple to one another.

In still another aspect (not shown), the puck 62 may be molded withinternal threads as a unitary structure, thereby eliminating one or moreof the plurality of nuts 96 and/or the washer 100.

In the event of an airplane overrun, the airplane tires likely will comein direct contact with one or more of the point anchors 60. Thus, thepoint anchor 60, with the exception of the pavement anchor 68 and themounting plate 70 preferably are formed from non-metallic materials, soas to prevent punctures, cutting, or other damage to the tires. At thesame time, the point anchor 60, and the puck 62 in particular,preferably are rigid enough to withstand jet blast forces under normalconditions without deforming plastically or failing. Thus, in oneaspect, the puck 62 may be a non-ductile injection molded glass fillednylon, such as a 33% glass filled nylon having a fracture stress f_(u)of about 21,000 psi and an ultimate strain ε_(u) of about 4.5%. Forexample, the puck 62 may be made of a 70G33HSIL NC010 nylon sold byDuPont under the trademark ZYTEL. Other suitable materials include, butare not limited to, plastic polymers that are relatively stiff,including, e.g., natural acrylonitrile butadiene styrene (ABS), glassfilled ABS, natural polypropylene, glass filled polypropylene, and highdensity polypropylene (HDPE).

Similarly, the rod 64, nuts 96, and washer 100 also may be made ofnon-metallic materials. The rod 64 may be high-strength fiberglass, thenuts 64 also may be fiberglass, and the washer may be made of nylon.Other materials, including other plastic polymers, may be used for eachof these components, as well as for the puck 62, as would be appreciatedby one of ordinary skill in the relevant art, provided those materialscause the point anchor 60 to behave as follows under different loadingconditions:

Under normal service operation, the loads from a top surface of thecover slab 56 may be transferred to the underside 86 of the puck 62,which is embedded in the slab 56, due to the cap 76 bearing against thetop face of the slab 56. Bearing forces may be idealized as a uniformlydistributed load, as shown in FIG. 14, and that load may be transferredto the rod 64 through the stiffeners 88 and the hub 74. During normaloperation, each puck 62 may be configured to withstand an upliftingforce caused by jet blast of about 750 to about 3000 lbs, and in oneaspect, about 1,500 lbs. Thus, the system 50 may include a plurality ofpoint anchors 60 in order to distribute the jet blast force and to keepthe maximum loading on any one point anchor 60 at or below the loadthreshold. For example, a greater number of point anchors 60 may bedisposed along an edge closest to and perpendicular to the runway ortaxiway, since the largest jet blasts may be experienced there. Inanother example, a plurality of point anchors may be disposed in a gridof substantially perpendicular rows and columns, a grid of staggeredrows and/or columns in which adjacent row or column elements are offsetfrom one another rather than being inline, or some other generallyuniform distribution.

In still another example, as seen in FIGS. 15 and 16, the bed may bedivided into a plurality of zones alternating between closely anchoredand widely anchored zones. The anchors in both zones in FIG. 15 arearranged in a square grid of aligned rows and columns. In contrast, theanchors in both zones in FIG. 16 are arranged in a diamond pattern,whereby successive rows and/or columns of anchors are offset from oneanother. It will be appreciated that an EMAS may include both square anddiamond grid layouts, as well as other arrangements of point anchors.

Additionally, in both figures, a first zone nearest an end of the runwayincludes anchors more closely spaced than in a successive second zone,although it will be appreciated that the arrangement of zones may bereversed. It also will be appreciated that an EMAS may include more thantwo zones of varying arrangements, where the zones may be of equal orunequal lengths.

Spacing between point anchors 60 may be determined by the sizing of theanchors, the characteristics of the EMAS arrestor bed (e.g., a thicknessof a slab cover), and the uplift loads that may be generated by thedesign fleet of each individual airport, e.g., smaller airports may notrequire the point anchors 60 to be as closely spaced since smalleraircraft normally generate less upward lift.

In one aspect, a spacing of between about 2.0 feet and about 6 feet, orbetween about 2.5 feet and about 5 feet, between point anchors 60 may besufficient. In another aspect, the spacing may vary based on distancefrom the jet blast. For example, the bed may be divided into multiplezones, with the zones closer to the jet blast having pucks 62 that aremore closely spaced than zones spaced further from the jet blast. In aspecific example, the bed may be divided in half, with the half closerto the jet blast having pucks 62 spaced about 2.5 feet apart and thehalf further from the jet blast having pucks 62 spaced about 5 feetapart.

FIG. 17 depicts a fringe plot representing deflections within the puck62 when subjected to a 1,500 lbf upload force. Peak displacements occurbetween the stiffeners 88 proximate the outer periphery 90 of the puck62 and are less than 0.1 inch. Such displacement levels may beconsidered negligible and further may represent elastic deformations,such that they may not have any negative impact on the serviceabilityperformance of the EMAS 50 nor degradation of the embedment puck 62itself. FIG. 18 depicts the stresses on puck 62 during the same loading.Stresses are generally under 10,000 psi, with a peak stress of less thanabout 16,000 psi, both of which are well below the design limit of about21,000 psi. Thus, under normal service operation, the puck 62 resiststhe upload forces associated with typical jet blast loads whileremaining relatively undeformed. Similarly, stresses are low enough thatdeformations may be elastic and, thus, the deformations are completelyreversible once loading is removed.

Under extreme uplift loading conditions, the puck 62 is configured tobreak and fail at one or more predetermined locations when apredetermined load amount is reached. For example, the puck 62 may failat the fuse 106, and specifically at one or more of the ribs 112. Thoseelements may remain essentially undeformed until failing in shear oncethey are overloaded. As such, the fuse 106 may separate from the rest ofthe puck 62, e.g., along the fracture path depicted in FIG. 13. Due tothe factor of safety built in to the puck as a result of its design andchoice of materials, fracture may not occur until the puck 62experiences an uplift load about 65% greater than the standard operatingload. Thus, as a result of failing at a predetermined location,inspection of pucks 62 for overloading and subsequent replacement orrepair may be simplified.

In addition to failing at the fuse 106, the point anchor 60, by way ofmaterial choice and design, may be configured to fail at one or moreadditional locations, although such failure may occur at higher loadsthan the failure load of the fuse 106. Such additional failure modes mayinclude: 1) punching failure of the topcoat 58 and/or slab 56 by thepuck 62 in the vicinity of the puck 62; 2) stripping of the threads 94,98 of one or both of the rod 64 and the nuts 96; 3) fracturing of therod 64; and 4) pulling-out failure of the pavement anchor 68 thatattaches the point anchor 60 to the underlying pavement. The EMAS 50preferably employs a balanced design, such that these failure modes aregenerally listed in increasing order of the loading required to causesuch failures. Thus, as can be seen, failures of the point anchor 60proximate a top of the EMAS 50 are more likely to occur first, whichagain simplifies inspection and repair since those failed elements canbe replaced without having to remove all of the aggregate 54, slab 56,and topcoat 58 around the point anchor in order to reach the pavementwhere the anchor 68 has pulled out.

Under airplane overrun conditions, the point anchor 60 is configured todeflect away from the airplane tire and/or to fracture at one or morelocations. For example, FIGS. 19 and 20 depict the results of two finiteelement overrun simulations in which an airplane tire penetrates theEMAS 50 by 6 inches and 12 inches, respectively. From those simulations,it can be seen that the point anchors act as breakaway elements duringan overrun event and do not cause damage to the tires that run overthem. In the shallower overrun event of FIG. 19, the puck 62 isdisplaced forward by the tire, while staying connected by the rod 64.Eventually, the puck 62 fractures at the fuse 106, while the cap 76further fractures at multiple locations, including along the score marks80. Similar failure modes are seen for the deeper overrun event of FIG.20. In that latter event, it also will be seen that the tire displacesthe aggregate and slab 56, forcing the slab 56 vertically upward. Thatdisplacement may apply sufficient uplift to cause fracturing of the fuse106 even before being contacted by the tire. Thus, the cap 76 mayprovide little to no resistance to the tire, further reducing thelikelihood that the cap damages the tire. As such, it may be understoodthat a primary focus of the point anchor 60 is to keep the aggregate 54and slab 56 in place, while the goal of slowing down the airplane in anoverrun event is handled mainly by the aggregate 54 and slab 56.

In another aspect, one of the nuts 96 may be metallic. Alternatively,the puck 62 may include an embedded metallic component, while remainingprimarily non-metallic. As such, it may be possible to locate the pointanchors 60 using a metal detector, even when covered by the slab 56and/or the topcoat 58.

The usage of point anchors 60 in the EMAS 50 may ease construction ofthe arrestor bed, including generating time savings during installationand repair. Without having to work around geogrid sections alreadyinstalled in the bed, the filling, compacting, and leveling of theaggregate 54 in the current system and method may occur more quicklythan in previous installations and ultimately may result in a slab 56having a more uniform thickness to provide more consistent arrestingcharacteristics. Additionally, rather than having to excavate largesections of the arrestor bed, full replacement of a point anchor 60 mayonly require excavating a small area in order to reach the anchor 68 atthe bottom of the bed. Still further, if the rod 64 remains intact butthe puck 62 fractures in one or more locations, it may be possible toreplace just the puck 62 without any excavation or by only excavating afew inches of the bed. Such time savings may be particularly importantwhen applied to busy runways that cannot remain closed for long periodsof time. Moreover, because the puck 62 may be embedded underneath thetopcoat 58, it may be possible to drive snow removal equipment over theEMAS 50 without causing damage to any of the pucks 62, therebymaintaining the integrity of the EMAS 50.

Additionally, the use of the point anchors 60 in the EMAS 50 may improvethe performance of the EMAS during overrun events. Arrestor beds thatemploy the point anchors 60 may have a uniform arresting performance,regardless of a rolling direction of the aircraft tires.

Turning to FIG. 21, the following method 200 may be employed to installthe EMAS 50 at the end of a runway. The method 200 may include securing202 the point anchors 60 to the pavement or other base of a bed, e.g.,through the use of a pavement anchor 68 passed through a mounting plate70 at a distal end 72 of the rod 64 and then embedded in the pavement orbase. Before or after the securing 202 step, the method 200 also mayinclude securing 204 the rod 64 to the point anchor 60. Additionally,the method 200 may include filling 206 the bed area with aggregate 54.The method 200 also may include adjusting the puck 62 relative to therod 64, e.g., by rotating it along the threading to raise or lower it,until a desired puck position is reached.

After the filling 206 of the bed area with the aggregate 54, the method200 includes compacting 208 and leveling 210 the aggregate 54 until adesired height is reached. As a result of the compaction, the aggregatemay become divided into a plurality of horizontal layers generallystacked one above the other. For example, the aggregate may include afirst section and a second section, where the first section is disposedbelow the second section, and the second section is in contact with aseparation layer installed above the aggregate. The second section maybe better compacted, such that it may be denser than the first section.

After that, the method 200 may include installing 212 the separationlayer to prevent intrusion of slab slurry into the aggregate. In oneaspect, the separation layer may be a geotextile fabric, although otherseparation layer materials may be employed, such as a polypropyleneplastic sheet, as would be appreciated by one of ordinary skill in therelevant art. The method 200 may further include coupling 214 the puck62 to the proximal end 66 of the rod, e.g., through use of the threading94, 98, the nuts 96, and the washer 100. Optionally, the method 200 alsomay include attaching 216 a top plug over the puck 62.

Following the installing step, the method 200 may include pouring 218slab material 56 onto the bed. The slab material may be in the form of acementitious slurry, such that it may flow underneath the embedment puck62 as it is poured, filling in the spaces between the stiffeners 88. Themethod 200 then may include screeding 220 or otherwise leveling the slabsuch that the slab is at or above the upper surface 78 of the puck 62.For example, the slab 56 may be poured to a height that substantiallycovers the puck 62, such that the puck 62 is embedded within the slab56.

In one aspect, the slab 56 may comprise a single material such ascellular concrete or CLSM. In another aspect, the slab 56 may comprisemultiple materials such as cellular concrete and CLSM. In this latteraspect, the multiple materials may be poured as multiple zones withinthe EMAS 50. For example, CLSM may be used to form the portion of theslab 56 closest to the runway, i.e., an entry portion of the EMAS 50,and the cellular concrete may be used to form the portion of the slab 56farthest from the runway. In another aspect, the multiple materials mayform alternating zones perpendicular to the direction of the runway.Still other slab configurations employing multiple materials may bepossible.

After the slab 56 has cured sufficiently, the method 200 may includeoverlaying 222 the topcoat 58 to produce a finished EMAS 50.

The rod 64 may be sufficiently rigid that it may remain substantiallyvertical under its own weight after being secured to the underlyingpavement or base of the bed. In another aspect, a support sleeve may beplaced around the rod 64 in order to position it vertically. After theaggregate 54 is placed, the sleeve may be removed, leaving the rod 64 inthe desired final location. In this alternative, the puck 62 may not becoupled to the rod 64 until after the sleeve is removed.

In an alternative embodiment, as seen in FIG. 22, the method 300 mayinclude filling 302 the bed area with the aggregate 54, then compacting304 and leveling 306 the aggregate 54, and installing 308 a separationlayer. The method 300 next may include boring or pressing 310 throughthe aggregate to the foundation of the bed, followed by securing 312 thepavement anchors 68 to the underlying pavement or base of the bed, e.g.,joining the rod to the pavement anchor using a coupler, and securing 314pavement anchors 68 to their respective rods 64. The method 300 also mayinclude coupling 316 the puck 62 to the proximal end 66 of the rod,e.g., through use of the threading 94, 98, the nuts 96, and the washer100, such that an underside 86 of the puck 62 rests on or just above thetop of the aggregate 54. Although shown as following the securing steps312, 314, the coupling step 316 alternatively may precede either or bothof those securing steps. In either event, the method 300 also mayinclude adjusting the puck 62 height relative to the rod 64, e.g., byrotating it along the rod threading to raise or lower it, until adesired puck height is reached. Optionally, the method 300 also mayinclude attaching 317 a top plug over the puck 62.

The method 300 then may include pouring 318 slab material 56 onto thebed. The slab material may be in the form of a slurry, such that it mayflow underneath the puck 62 as it is poured, filling in the spacesbetween the stiffeners 88. The method 300 then may include screeding 320or otherwise leveling the slab such that the slab is at or above theupper surface 78 of the puck 62. For example, the slab 56 may be pouredto a height that substantially covers the puck 62, such that the puck 62is embedded within the slab 56.

After the slab 56 has cured sufficiently, the method 300 may includeoverlaying 322 the topcoat 58 to produce a finished EMAS 50.

Turning now to FIG. 23, one example of the normalized drag force versusdistance is depicted for a physical test involving an aircraft tiretraveling through an EMAS bed with a cellular concrete cover layer. Asseen in that figure, the normalized drag force tends to decrease as theaircraft travels through the EMAS as a function of speed during thetest. That normalized force also remains generally between 0.5 and 0.9,indicating that the aircraft tire experiences generally constant dragloading, and further indicating the absence of any extreme loadingeffects.

FIG. 24 depicts several examples of actual versus predicted failuremodes of the puck 62, when those pucks were embedded in an EMAS of thesort described herein and were exposed to an aircraft tire travelingthrough the EMAS as would be likely during an overrun event. As thefigure illustrates, the pucks failed at various points along the cap 76.While not shown in this figure, none of the pucks 62 damaged orotherwise harmed the test tire.

From this testing, it can be observed that point anchors 60 are usablewith both cellular concrete and CLSM as the slab material. Also, thosepoint anchors 60 are much easier to work with than geogrid, providingease and rapidity of installation, good breakaway performance, and alack of apparent aircraft tire damage.

Turning now to FIGS. 25-34, additional variants to the slab portion ofthe EMAS are contemplated. In particular, the underside of the slab maybe specifically configured to include voids between the aggregate andthe overlying slab. Each of the variants described herein may beemployed with the various aggregate configurations discussed above, orthey may employed on top of other aggregates as would be appreciated bythose skilled in the relevant art.

FIGS. 25 and 26 illustrate a slab 400 having an underside 402 thatincludes a plurality of ribs 404 depending downwardly therefrom. Eachrib 404 may have a first thickness t₁, while the portions 406 of theslab 400 between the ribs 404 may have a second thickness t₂. In oneinstance, the first thickness may be as large or larger than the secondthickness. For example, the first thickness may be between about 1½ andabout 3 times that of the second thickness or, in another example, abouttwice that of the second thickness. The ribs 404 may be tapered, suchthat a free distal end 408 may have a width smaller than the width at aproximal end 410. Each side 412 may form an angle θ with the distal end408, where that angle preferably is between about 45 degrees and about90 degrees, and in one embodiment is about 60 degrees. Additionally thedistance d₂ of the distal end 408 may be different than a distance d₁ ofthe portions 406 between ribs 404. For example, the distance d₁ may beat least as large as the distance d₂ and, preferably, is larger thanthat distance. FIG. 26 illustrates that, in one instance, the distanced₁ may be about twice the distance d₂.

Ribs 404 may be substantially parallel to one another along a length ofthe EMAS. As seen in FIG. 25, the ribs 404 may be substantially linearalong their lengths, although other variations are within the scope ofthis disclosure. For example, ribs may be zig-zagged, sinusoidal, orotherwise curvilinear, while still remaining substantially parallel toone another.

Turning now to FIGS. 27 and 28, it will be appreciated that the ribs 404may be oriented in one or more ways along an EMAS relative to adirection of travel of an aircraft, i.e., relative to a direction of arunway adjacent to which the EMAS is installed. FIG. 27 illustrates thatthe ribs 404 may be oriented generally perpendicular to that directionof travel, whereas FIG. 28 alternatively illustrates that the ribs 404may be oriented generally parallel to the direction of travel. In yetanother alternative, the ribs 404 may be offset at some angle betweenthe orientations of FIGS. 27 and 28, e.g., at a 45 degree angle relativeto both.

FIGS. 27 and 28 also illustrate that the EMAS may be divided into aplurality of zones, including a first zone 414 adjacent an entrance 416to the EMAS and a second zone 418 adjacent the first zone 414. The firstzone 414 may include ribs 404 a more closely spaced together than ribs404 b in the second zone 418, which may result in increased resistanceand deceleration of aircraft tires passing through the first zone 414 ascompared to the second zone 418. Alternatively, spacing between ribs mayvary within a zone, e.g., from one set of ribs to another, rather thanhaving multiple distinct zones where rib spacing is substantiallyidentical within a given zone.

Additionally, the ribs 404 a, 404 b may serve to stiffen theirrespective slab zones 414, 418 and enhance bending strength. As a resultof the increased number of ribs 404 a proximate the entrance 416 to theEMAS, the first zone 414 may exhibit better strength characteristics,thereby better resisting uplift loads due to jet-blast and wind, whichmay be significant when aircraft are pointed away from the EMAS, e.g.,when using the end of the runway at which the EMAS is located as a startend for aircraft takeoffs.

Turning to FIGS. 29-31, in another aspect, the slab 430 may include anunderside 432 with a waffle-shaped pattern 434 depending downwardlytherefrom. The waffle-shaped pattern 434 may comprise a first series ofribs 436 depending downwardly from the underside 432 in a firstdirection and a second series of ribs 438 depending downwardly from theunderside 432 in a second direction, where the second direction may beperpendicular to or otherwise angled with respect to the firstdirection.

In one aspect, the first and second series of ribs 436, 438 may besimilarly shaped, e.g., having a similar shape as the ribs 404 describedabove. For example, ribs 436 may have a first thickness t₃, while theportions 440 of the slab 430 between the ribs 436 may have a secondthickness t₄. Ribs 438 similarly may have a first thickness t₅, whileportions of the slab 430 between ribs 438 may have a second thicknesst₆. The thickness t₃ may be substantially equal to the thickness t₅, andthe thickness t₄ may be substantially equal to the thickness t₆.Alternatively the respective first thicknesses may be different and therespective second thicknesses may be different, although a total of thefirst and second thicknesses for each series of ribs 436, 438 may besubstantially equal. In still another embodiment, the first thicknessesmay be different than the second thicknesses and the total of the firstand second thicknesses of the first series of ribs 436 may be differentthan the total of the first and second thicknesses of the second seriesof ribs.

Additionally, each of the first series of ribs 436 and the second seriesof ribs 438 may be tapered, such that a free distal end 444, 446,respectively, may have a width smaller than the width at a proximal end448, 450, respectively. Each side 452 of the first series of ribs 436may form an angle α with the distal end 444, and each side 454 of thesecond series of ribs 438 may form an angle β with the distal end 445.Each of angles α and β may be between about 45 degrees and about 90degrees, and in one embodiment each is about 60 degrees.

Additionally the distance d₄ of the distal end 444 of the first seriesof ribs 436 may be different than a distance d₃ of the portions 440between ribs 436. For example, the distance d₄ may be at least as largeas the distance d₃ and, preferably, is larger than that distance. Thesecond series of ribs 438 may be similarly configured with regard to therespective distances d₆ and d₅. FIG. 30 illustrates that, in oneinstance, the distance d₃ may be between about one and two times aslarge as the distance d₄. Conversely, the distance d₅ may be betweenabout 3 and about 5 times the distance d₆. The respective distances d₁through d₆ may be modified as needed, e.g., in order to customize thefrangibility of the respective slabs 400, 430 or in order to change theshapes of the waffle pattern. For example, the ribs 436, 438 in FIG. 29result in a waffle pattern in which a central recessed area 456 isrectangular. Alternatively, FIGS. 32 and 33 depict a waffle pattern inwhich the ribs 436, 438 are sized and spaced such that the centralrecessed area is square.

Turning now to FIGS. 32-34, it will be appreciated that the first andsecond ribs 436, 438 may be oriented in one or more ways along an EMASrelative to a direction of travel of an aircraft, i.e., relative to adirection of a runway adjacent to which the EMAS is installed. FIG. 32illustrates that the first ribs 436 may be oriented generally parallelto that direction, while the second ribs 438 are oriented generallyperpendicular to that direction. Alternatively, FIG. 33 illustrates thatboth ribs 436, 438 may be offset at some angle relative to the directionof travel e.g., at a 45 or 135 degree angle, although other offsetamounts are possible. Additionally, in FIG. 33, the first and secondribs 436, 438 remain generally perpendicular to one another. In anotheraspect, the ribs may be angled acutely or obtusely to one another.

FIG. 34 illustrates that the EMAS may be divided into a plurality ofzones, including a first zone 458 adjacent an entrance 460 to the EMASand a second zone 462 adjacent the first zone 458. The first zone 458may include first and second ribs 436 a, 438 a more closely spacedtogether than ribs 436 b, 438 b in the second zone 462. FIG. 34 furtherillustrates that the relative spacing between first and second ribs mayvary from the first zone 458 to the second zone 462, e.g., causing theshape of the waffle patterns to change from generally square torectangular. Rib alignment and sizing within each zone and between zonesmay be modified to achieve similar outcomes discussed above with regardto the arrangements of FIGS. 27 and 28.

In another aspect, rib configuration may vary from zone to zone, wherebya first zone may include only ribs and a second zone may includewaffle-patterned ribs or vice-versa. In still another aspect, the EMASmay include one or more flat zones without ribs or waffles where theflat zone(s) may be disposed ahead of the other zones, between one ormore other zones, or after the other zones. In yet another aspect, thewaffles may be something other than rectangular. For example, FIG. 35depicts an EMAS with various circular waffles. Other shapes for theunderside of the slab are possible, as would be appreciated by one ofordinary skill in the relevant art.

The rib or waffle configurations discussed above may improve upon flatslabs that are installed directly on top of an aggregate by providingfor easier punch-through by an aircraft tire and for less confinement tothe underlying aggregate. In particular, the latter benefit may permitincreased energy transfer from the aircraft into the aggregate,permitting the EMAS to arrest the aircraft more quickly.

Such benefits may be achieved by causing the ribs or waffle patterns todefine a plurality of voids between the slab and the underlyingaggregate. In this regard, it should be understood that a void does notnecessarily refer to an empty or air-filled space between the twostructures. Rather, a void should be considered one or more areasbetween the aggregate and slab that are filled with something other thanslab. FIG. 36 depicts an EMAS with a first void 464, where that void isair-filled. FIG. 37 depicts an EMAS with one or more second voids 466,where the voids 466 are defined by a formwork 468 that provides a shapeof the resulting ribs in the slab, as well as an air-filled portion 470between the formwork 468 and the aggregate. FIG. 38 depicts stillanother EMAS with one or more third voids 472, where the third void 472is defined by a formwork 474 resting on the aggregate and substantiallycompletely filling an area between the aggregate and the slab. In stillanother aspect, the voids of FIGS. 36 and 37 may replace one or more ofthe air-filled portions with a different medium, e.g., a lightweightfoam or plastic.

With regard to FIGS. 37 and 38, the formworks 468, 474 may comprise amaterial that provides sufficient strength to support the slab whilebeing brittle enough to fracture easily under the loads caused byaircraft tires passing through the EMAS. For example, the formwork maycomprise a plastic or polymer with brittle characteristics including,but not limited to polystyrene, polyactic acid (PLA), polyvinyl chloride(PVC), polymethyl methacrylate, or other acrylics.

As discussed above, one method for fabricating a slab is to pour theslab material, e.g., CLSM, cellular concrete, or another slab material,on top of the aggregate. In those cast-in-place (CIP) instances, themethod may be modified to include the step of positioning a formwork ontop of the aggregate prior to pouring the slab. As such, the slabmaterial may flow to conform to the shape of the formwork, resulting information of both the slab and the underlying void. In the event thatthe void includes some medium other than air and in addition to theformwork, that additional medium may be installed on top of theaggregate or in the spaces of the formwork, prior to installing theformwork.

As an alternative to CIP methods, the slab may be pre-cast (PC) into itsdesired shape prior to installing the slab on top of the aggregate.Pre-casting may be favorable, because it reduces the time needed toconstruct the EMAS, which may be significant when that EMAS is beinginstalled at the end of active runways or when that installationrequires shutting down an active runway. In such instances, the slabmaterial may be poured into a mold forming the desired underside shapeand permitted to cure. Once cured, the slab may be separated from theformwork, permitting just the slab to be installed on top of theaggregate. Alternatively, the formwork may remain adhered to orotherwise in contact with the poured slab, with both components beinginstalled on top of the aggregate, such that the formwork becomes apermanent component of the EMAS.

Any of the slabs discussed above also may be secured to the EMAS usingone or more of the securement structures discussed herein, or usinganother securement method as would be appreciated by those of ordinaryskill in the relevant art. For example, FIGS. 39 and 40 illustrate oneexample of a ribbed slab being installed using geogrid, and FIGS. 41 and42 illustrate an example of a ribbed slab being installed usingpuck-type retainers. In both examples, the geogrid and the pucks areinstalled in-line with the ribs, which may increase the thickness of theslab through which those attachment mechanisms pass, thereby increasingtheir effectiveness. At the same time, a geogrid, puck, or otherattachment mechanism may be installed through other parts of the slab.Additionally, in both examples, the void is depicted as a single,uniform medium, which may be air or another medium such as polystyrene.As discussed above, however, the void may comprise a plurality ofdifferent media, which may have no effect on the method of attaching theslab to the rest of the EMAS.

Slab structures that include the ribs or waffle structures describedherein may be stiffer and lighter than an equivalent flat slab and,relatedly, may be formed using less material than a flat slab. At thesame time, such slabs exhibit better strength characteristics withregard to resisting uplift loads on the slab. For example, the inclusionof ribs or a waffle-like structure may serve to stiffen the slab andincrease its bending strength as compared to a flat slab. As a result,fewer anchors (e.g., geogrid or the puck anchors discussed herein) mayneed to be used to secure the slab, further reducing materials andconstruction time. Still further, as seen in FIG. 43, the formation ofthinner slab regions between the ribs may result in comparatively weakerregions that permit punch-through or fracturing of the slab during anoverrun event by smaller and/or lighter aircraft, thereby permitting asingle EMAS to be effective for a larger range of aircraft than a flatslab.

Furthermore, as seen in FIG. 44, the inclusion of one or more voidsbetween the aggregate and the slab may permit or enhance thedisbursement of aggregate material, i.e., reducing confinement of thatmaterial. That improved behavior may lead to the EMAS having a moreuniform response to a wider range of vertical loads caused by a widerrange of tire sizes and aircraft. The size and shape of the voids alsomay be customized to tune the level of confinement to the airport beingserviced by the EMAS. For example, regional or local airports may haveprimarily smaller aircraft use their runways as compared tointernational airports, where the latter may require a larger degree ofaggregate displacement to disperse energy, as well as a stiffer slab tobetter resist updrafts caused by larger engines. Alternatively, lessconfinement of the aggregate may result in a softer effective response,as though a softer grade of material is being used. As such, allowingfor less confinement in an EMAS designed to service smaller planes maypermit deeper penetration and greater arresting forces.

Turning now to FIGS. 45-50, and further with regard to the cast-in-placeand pre-cast slabs discussed above, the slabs may be formed by aformwork system 500 comprising a plurality of abutting and potentiallyoverlapping formworks 502 a-d. One common feature to the formworks shownin these figures is that each formwork is designed to remain with theresultant slab portion 504 a-d that it forms. Additionally, eachformwork includes an anchor point 506 a-d to assist in securing anembedment puck such as the anchors 60 described herein. Such anchors maybe modified to include a plurality of legs 508 to assist in aligning theanchors 60 in a desired orientation.

FIGS. 45 and 46 illustrate a first aspect of one such formwork system500 a. The system includes a plurality of formworks 502 a-d that aredesigned to form the ribs or waffle patterns described above, eachformwork having an underside 510 shaped to form the void 512 between theaggregate 514 resting on top of the pavement 516 and the resulting slab504. Each formwork also has an upper side 518 configured to receive theslab material. Additionally, a first formwork 502 a includes a firstside 520 configured to abut an opposing side 522 of a second, or firstadjacent formwork 502 b. The first formwork 502 a also may include asecond side 524 configured to abut an opposing side 526 of a thirdformwork 502 c that is adjacent in a different direction, e.g.,perpendicular to the first adjacent formwork 502 b. Still further, theformwork system may include at least a fourth formwork 502 d adjacent tothe second and third formworks 502 b, 502 c. As seen in FIG. 45, thefourth formwork 502 d also may be generally diametrically opposed to thefirst formwork.

In one aspect, the abutting sides may be substantially linear. Inanother aspect, the abutting sides may have curvilinear, jagged, orother shapes, provided that the sides are generally mirror images of oneanother to facilitate abutment.

When abutting, at least one opening 528 may be defined between theadjacent formworks. For example, in FIG. 45, each of the formworks 502a-d includes a concave notch 530 a-d. As such, the abutting formworksdefine a circular opening 528. Other notch shapes are possible, as wouldbe appreciated by one of ordinary skill in the relevant art, e.g., alinear segment that effectively removes a triangular corner of theformwork such that the abutting formworks define a square or otherrectangular opening.

As discussed above, the EMAS may include a plurality of point anchors 60to secure the slab 504 to the underlying pavement 516 via a strap or rod64. The opening 528 defined between the formworks 502 a-d may be sizedto accommodate that strap or rod 64, such that the point anchor 60 maybe generally centered over the intersection between abutting formworks502 a-d. As such, each point anchor 60 may operate to secure at least aportion, e.g., a corner, of each formwork 502 a-d and its respectiveslab 504 a-d to the pavement 516.

As discussed above, each formwork 502 a-d also may include a respectiveanchor point 506 a-d configured to receive an anchor leg 508 defined byor in communication with the point anchor 60. In addition to acompressive force generated between the point anchor 60 and the slabportions 504 a-d, the anchor legs 508 may further secure the pointanchor 60 to those slab portions 504 a-d and also may prevent rotationalmovement of the point anchor 60 relative to the slab 504.

Alternatively, rather than extending downward from the point anchor 60,the anchor legs 508 may be secured in and extend upwardly from theaggregate 514 prior to installation of the formworks 502 a-d and theirrespective slabs 504 a-d. The anchor points 506 a-d then may be loweredaround the anchor legs 508, serving to accurately position the slabs 504a-d in the EMAS.

Also as discussed above, the formworks 502 a-d may be made of a lowstrength, brittle material in order to fracture relatively easily duringan overrun event. The region 532 underlying the point anchor 60 may bereinforced or formed of a higher strength material in order to resistfracturing caused by the compressive forces exerted by the point anchor60.

In addition to providing for a securement point for the point anchors,the openings 528 between formworks may allow for easy access to thoseanchor systems, permitting rapid inspection and more targetedmaintenance as compared to systems in which the slab is a continuous bedof material. The openings 528 also may reduce the time needed toconstruct the EMAS bed, as they may reduce or eliminate the need todrill separate openings for the strap or rod 64 and the anchor legs 508.For example, a column having the same or a similar cross-section to theanchor points 506 a-d and/or the opening 528 may be placed in thoseopenings prior to pouring of the slab. As the slab material then ispoured, it may flow around those columns so that a clear path isestablished through the slab to those openings, reducing or eliminatingthe need for subsequent drilling to create those paths.

Additionally, although the formworks 502 a-d in FIG. 45 are depicted ashaving a single anchor point 506 a-d and notch 530, it will beappreciated that each formwork may include multiple such anchor pointsand notches. For example, a formwork may include similar features in oneor more other corners of the formwork, at one or more points morecentrally located along the sides of the formwork, or at one or morelocations more internally defined away from the sides of the formwork.

Turning now to FIGS. 47 and 48, in another aspect, the formworks 502a-d, in addition to abutting one another along their lengths, also mayoverlap at distinct points, e.g., at the corners 534 a-d. Rather thanhaving a plurality of notches defining an opening, these formworks eachmay include a protrusion 536 a-d extending from the corners 534 a-d. Asseen in FIG. 48, the protrusions 536 may extend to different depths andat different angles relative to both an underside 510 and an upper side518 of the formworks 502 a-d, thereby permitting the protrusions tosubstantially stack on top of one another when their slab portions 504a-d are installed in the EMAS.

Each protrusion 536 a-d may include one or more complementary openings538 a-d that may align vertically when the formworks 502 a-d and theirrespective slabs 504 a-d are installed in the EMAS, those openings 538a-d combining to provide a pathway for the strap or rod 64. Eachformwork 502 a-d also may include one or more other openings (not shown)for receiving the anchor legs 508 to position the formworks 502 a-d inthe proper location within the EMAS. Those openings may align with oneanother so that an anchor leg 508 may pass through multiple openings.Alternatively, one or more of those openings may be sized and/orpositioned such than an anchor leg passes through that anchor leg only.

Turning now to FIGS. 49 and 50, in still another aspect, the formworks502 a-d may be configured to have one or more sides that overlap withadjacent formworks. For example, the first side 520 of the firstformwork 502 a may overlap with the first side 522 of the adjacentformwork 502 b, and the second side 524 may overlap with the first side526 of a different adjacent formwork 502 c. As with the overlappingprotrusions in the aspect discussed above, each side may include one ormore complementary openings 538 a-d that align vertically when theformworks 502 a-d and their respective slabs 504 a-d are installed inthe EMAS in order to provide a pathway for the strap or rod 64.

In the overlapping aspects, the formworks may be used in cast-in-placeinstallations, so that slab material may be poured on top of all of theoverlapping portions, i.e., the protrusions 536 a-d or the sides, oncethe formworks 502 a-d are installed. In pre-cast installations, theslabs may be formed into the formworks, but the slabs may includeremovable or permanent walls (not shown) that separate the overlappingportions from a remainder of the formworks. In this way, there may notbe any precast slab material poured over the overlapping portions thatwould inhibit later stacking or overlapping of those portions. In thatcase, the installation process then may include filling in the areaabove the overlapping portions with slab material on-site, and after theslabs 504 a-d have been installed.

Alternatively, all but one of the overlapping formworks 502 a-d mayinclude walls that separate their overlapping portions from a remainderof the formwork. The overlapping portion that would be uppermost in theoverlapping process may not include any such wall such that thatformwork may receive slab material when being cast, thereby permittingoverlapping of the portions and reducing or eliminating a need foradditional pouring of slab material after installation of the slabs 504a-d.

Turning now to FIGS. 51-61, it will be appreciated that a geogrid mesh600 can be used instead of or in addition to the puck retainersdescribed above, in order to connect a cover layer 602 of the EMAS to anunderlying pavement 604. In such instances, the geogrid 600 also mayextend through an aggregate layer 606 and/or a slab layer (not shown).The geogrid 600 may be installed in an overrun direction of the bed,although it also may be installed perpendicular to or at angle to theoverrun direction.

In order to function properly, the geogrid 600 should be connected at aproximal end 608 and a distal end 610 to the underlying pavement 604 andthe cover layer 602, respectively. Conventionally, geogrid is installedwith point anchors securing the proximal end 608 to the pavement 604 andrigid straps between the anchors so as to provide uniform confinement ofthe geogrid between point anchor locations. Installation of each pointanchor requires drilling a hole in the pavement 604 and then driving theanchor through the geogrid and the pavement 604, which is a laborintensive and lengthy process. As seen in FIG. 51, the anchors may bereplaced by the use of an adhesive 612 to secure one or more sections ofgeogrid 600 to the pavement. In another aspect (not shown), the adhesivemay be used in conjunction with one or more anchors, although theadhesive may permit the use of fewer anchors than would be necessarywithout the adhesive.

The adhesive selected should substantially retain its holdingcharacteristics over time and under an extreme range of weatherconditions, should not degrade, and should provide sufficient strengthto resist projected loads. Exemplary adhesives include thixotropicadhesives such as bituminous-based adhesives, epoxies, or silicone-basedadhesives.

FIGS. 52-61 depict various methods for installing geogrid 600 usingadhesive. In each instance, the proximal end 608 of the geogrid 600 isbent at substantially a right angle relative to a central region 614 ofthe geogrid 600.

In FIGS. 52 and 53, a layer of adhesive 612 is applied to the pavement604, and the proximal end 608 is pressed into the adhesive and allowedto cure—with or without the addition of heat, depending on the type ofadhesive used. Optionally, an additional layer of adhesive then may beapplied on top of the first layer and the geogrid. The process then isrepeated as necessary in order to install additional sections of geogridwithin the EMAS bed. Once all geogrid sections have been installed, withthe central regions 614 being disposed generally vertically upward, thebed is filled with aggregate and overlaid with a slab, as discussedherein.

FIGS. 54 and 55 depict an aspect in which a supplemental bar or plate616 is added and positioned above the pavement 604 and the adhesive. Inthis aspect, a first layer of adhesive 612 a is applied to the pavement,the proximal end 608 is pressed into that first layer, a second layer ofadhesive 612 b then is added on top of the proximal end 608—eitherbefore or after the first layer is allowed to cure, the plate 616 ispressed into the second layer of adhesive 612 b, and that adhesive layeris permitted to cure. In one instance, the plate 616 has a width lessthan a width of the proximal end 608, and the plate 616 is disposedproximate an intersection 618 of the proximal end 608 and the centralregion 614 of the geogrid. In another instance, the plate 616 has awidth less than a width of the proximal end 608, and the plate 616 islocated anywhere along the width of the proximal end 608, provided thatall or at least a part of the plate 616 overlaps the proximal end 608.In still another instance, the plate 616 has a width equal to or greaterthan that of the proximal end 608, and the plate 616 is disposed eitherproximate or spaced from the intersection 618. Additionally, the plate616 is depicted in these figures as a flat, substantially planar member,although it alternatively may be an L-shaped, U-shaped, or other angledmember that secures and/or aids in orienting the central region 614 in agenerally vertical or other direction. The plate 616 may be sufficientlyrigid to prevent the geogrid 600 from peeling away from the adhesive 612and/or from forming stress concentrations relative to the adhesive 612.Exemplary materials for the plate 616 include steel, aluminum, andvarious rigid polymers. Additionally, the plate 616 may be formed so asto avoid such stress concentrations. For example, stress concentrationsmay form at the ends of each plate 616, so those ends may be enlarged orrounded as compared to a remainder of each plate 616.

FIGS. 56 and 57 depict an additional aspect in which the proximal end608 of the geogrid 600 is divided into one or more first portions 608 aextending laterally away from one side of the central region 614 and oneor more second portions 608 b extending laterally away from an oppositeside of the central region 614. First and second portions 608 a, 608 bmay have predetermined lengths, wherein the proximal portion 608 of thegeogrid may be segmented prior to delivery of the geogrid at theinstallation location. Alternatively, the proximal portion 608 may bescored at periodic intervals, permitting the installer to select thelocations at which to separate the proximal end 608 into first andsecond portions 608 a, 608 b. In still another aspect, the geogrid 600may arrive at an installation site as a single, unified piece, and theinstaller then may use some kind of cutting implement to section thegeogrid proximal end 608 into the first and second portions 608 a, 608 bat the time of installation. To install this geogrid, the installerfirst may deposit one or more regions of adhesive 612 on the pavement604. The geogrid may be prepared such that the first portions 608 a andthe second portions 608 b alternate and extend in opposite directions.Those portions 608 a, 608 b then are pressed into the adhesive andallowed to cure—with or without the addition of heat, depending on thetype of adhesive used. Optionally, an additional layer of adhesive thenmay be applied on top of the first layer and the geogrid. The processthen is repeated as necessary in order to install additional sections ofgeogrid within the EMAS bed. Once all geogrid sections have beeninstalled, with the central regions 614 being disposed generallyvertically upward, the bed is filled with aggregate and overlaid with aslab, as discussed herein.

FIGS. 58 and 59 depict a variation of the aspect of FIGS. 56 and 57 inwhich a plurality of supplemental bars or plates 616 a, 616 b aresituated on top of the geogrid proximal end portions 608 a, 608 b. Thosefigures depict the plates 616 a, 616 b as flat, substantially planarmembers, although they alternatively may be L-shaped, U-shaped, or otherangled members that secure and/or aid in orienting the central region614 in a generally vertical or other direction. Additionally, the plates616 a, 616 b are depicted in these figures as being discrete elementsgenerally equal in length to the lengths of their respective proximalportions 608 a, 608 b. In another aspect, the plates 616 a, 616 b may besubstantially longer than the geogrid proximal portions 608 a, 608 b.For example, plates 616 a, 616 b may span approximately an entire widthof the geogrid 600, or a distance sufficient to cover two of theproximal end portions 608 a or two of the proximal end portions 608 b,or approximately five portions, or approximately ten such portions, orapproximately twenty such portions. In this aspect, a first layer ofadhesive 612 a is applied to the pavement, the proximal end portions 608a, 608 b are pressed into that first layer, a second layer of adhesive612 b then is added on top of the proximal end portions 608 a, 608b—either before or after the first layer is allowed to cure, the plates616 a, 616 b are pressed into the second layer of adhesive 612 b, andthat adhesive layer is permitted to cure.

In each of the aspects shown in FIGS. 52-59, the geogrid 600additionally may be secured to the pavement 604 with one or morefasteners. Due to the inclusion of the adhesive, however, fewerfasteners may be required to provide equivalent adhesion for the geogrid600 than a similar system that does not include the use of adhesives.

Turning now to FIGS. 60 and 61, in still another aspect, a channel 620is formed in the pavement 604, the channel 620 being slightly wider thana width of the geogrid 600. An adhesive 612, e.g., a self-expandingadhesive, and the proximal end 608 then are placed in the channel 620.The adhesive then is permitted to cure. The process then is repeated asnecessary to install additional geogrid elements, and an aggregate thenis added around the geogrid elements. As seen in FIG. 61, the channel620 may have a depth at least as large as a width, or at least twice aslarge as a width, or at least 2.5 times as large as a width.

Turning now to FIGS. 62-68, additional modifications to the aggregateand/or slab layers may improve operability of the EMAS. While not shownin these figures, it will be understood that the EMAS may include atopcoat or covering of some kind, as well as one or more types ofanchoring systems, as such features as discussed in greater detailherein.

FIG. 62 depicts one aspect in which a first aggregate layer 700 ispoured on top of an underlying pavement 702. The aggregate is compactedand a first slab layer 704, either PC or CIP, is installed on top of thefirst aggregate layer 700. A second aggregate layer 706 then is pouredon top of the first slab layer 704 and compacted. A second slab layer708, either PC or CIP, then is installed on top of the second aggregatelayer 706. The aggregate layers 700, 706 may comprise the same materialand the same compaction method, e.g., using a bobcat, vibrator plate,etc. Alternatively, the aggregate layers may comprise differentmaterials and/or different compaction methods. FIG. 62 also illustratesthat the aggregate layers are approximately equal depths, although itwill be appreciated that they may be poured to different depths toprovide different arresting characteristics. For example, the firstaggregate layer 700 may be deeper than the second aggregate layer 706,or vice versa. It also will be appreciated that additional aggregateand/or slab layers may be added on top of or between the layers shown.

FIG. 63 depicts a second aspect in which a first aggregate layer 700 ispoured on top of the pavement 702 and compacted. A thin separation layer710 is installed on top of the first aggregate 700, and the secondaggregate layer 706 is poured on top of the separation layer 710 andthen compacted. Finally, the slab layer 704 is installed on top of thesecond aggregate layer, e.g., using one or more of the methods describedherein. In this instance, the separation layer 710 may be a relativelythin, relatively brittle or frangible material such as fiberglass, fibercement board, or rigid polypropylene, having a thickness between about 1mm and about 13 mm. Additionally, the first and second aggregate layersin this aspect are shown to be the same material, compacted using thesame method, and having substantially the same depth. It will beappreciated, however, the different aggregate materials, compactionmethods, and/or depths may be used for the different aggregate layers.It also will be appreciated that additional aggregate, separation,and/or slab layers may be added on top of or between the layers shown.

FIG. 64 depicts a third aspect in which a first aggregate layer 700 ispoured on top of the pavement 702 and compacted. A second aggregatelayer 706 is poured on top of the first layer and compacted, and a thirdaggregate layer 712 is poured on top of the second layer and compacted.Finally, the slab layer 704 is installed on top of the third aggregatelayer, e.g., using one or more of the methods described herein. In thisaspect, the aggregate layers may comprise different types of aggregates,e.g., different grades of glass foam aggregate or different types ofaggregate material generally. The aggregate layers may be compactedusing the same method, although it also is possible to compact one ormore of the layers using a different method. Additionally, the aggregatelayers are depicted as having substantially the same depth, although itwill be appreciated that one or more of the layers may have a differentdepth than the other layers. It also will be appreciated that additionalaggregate, separation, and/or slab layers may be added on top of orbetween the layers shown.

FIG. 65 depicts a fourth aspect in which a first aggregate layer 700 ispoured on top of the pavement 702 and compacted. A second aggregatelayer 706 is poured on top of the first layer and compacted, and a thirdaggregate layer 712 is poured on top of the second layer and compacted.Finally, the slab layer 704 is installed on top of the third aggregatelayer, e.g., using one or more of the methods described herein. In thisaspect, the aggregate layers may comprise the same type of aggregate,although one or more of the layers may comprise a different type ofaggregate as compared to the other layers. Also in this aspect,different compaction methods may be used on at least one of theaggregate layers. Additionally, the aggregate layers are depicted ashaving substantially the same depth, although it will be appreciatedthat one or more of the layers may have a different depth than the otherlayers. It also will be appreciated that additional aggregate,separation, and/or slab layers may be added on top of or between thelayers shown.

FIG. 66 depicts a fifth aspect in which a first aggregate layer 700 ispoured on top of the pavement 702 and compacted. A second aggregatelayer 706 is poured on top of the first layer and compacted, and a thirdaggregate layer 712 is poured on top of the second layer and compacted.Finally, the slab layer 704 is installed on top of the third aggregatelayer, e.g., using one or more of the methods described herein. In thisaspect, each of the aggregate layers may comprise a different aggregatecomposition and may be compacted using a different method, although atleast two of the layers may comprise the same composition and/orcompaction method. Additionally, the aggregate layers are depicted ashaving substantially the same depth, although it will be appreciatedthat one or more of the layers may have a different depth than the otherlayers. It also will be appreciated that additional aggregate,separation, and/or slab layers may be added on top of or between thelayers shown.

FIGS. 67 and 68 depict different overrun events for which the variousaggregate and slab stratifications may be particularly tailored. In FIG.67, a large tire may roll through the EMAS and penetrate both slablayers and both aggregate layers. This tire may benefit from theadditional, deeper aggregate and/or slab to provide the desired stoppingperformance. Alternatively, in FIG. 68, a smaller tire, e.g., connectedto a smaller aircraft, may roll through the EMAS and only penetrate thesecond slab layer 708 and the second aggregate layer 706, leaving thefirst slab layer 704 and the first aggregate layer 700 undisturbed. Insuch instances, it may not be necessary to remove the first slab layer704 and/or first aggregate layer 700 after an overrun event, reducingdowntime before the runway is operational or the EMAS is repaired, aswell as reducing the cost for such repairs. Similar results may obtainfor the other stratification examples discussed above. As such, the neteffect of a multi-layer system may be to allow an EMAS response toself-tailor to different sizes of aircraft, such that bed designeffectively becomes a several-in-one system design that can handlemultiple size classes of aircraft in ways close to their design ideals.

Turning now to FIGS. 69-78, the EMAS also may include one or more lidportions 750 on top of or instead of the slab. Each lid portion 750 maytake the form of a panel that is disposed on top of an aggregate layer752 and that additionally includes one or more anchors 754 for securingto the underlying pavement 756. An upper, exposed surface 758 of the lidportion 750 may be substantially flat. Conversely, an underside surface760 of the lid portion 750 may include one or more stiffening members762. The number, size, and orientation of the stiffening members 762 maybe adjusted for the particular EMAS installation in order to balanceincreased strength and stiffness for handling service loads caused byjet blast, wind, or other factors, with the need to provide forfrangibility and a desired aggregate confinement during overrun events.

In one aspect, as seen in FIG. 69, the stiffening members 762 may takethe form of a plurality of ribs 764 extending in a single directionalong the underside 760 of the lid 750. In another aspect, as seen inFIG. 70, the stiffening members may take the form of a first pluralityof ribs 764 a extending in a first direction and a second plurality ofribs 764 b extending in a second direction perpendicular to the firstdirection. Other configurations of stiffening members, including ribsoffset at non-perpendicular angles, circular ribs, curvilinear ribs,etc., may be employed, provided the desired strength to frangibilitybalance is achieved. The choice and thickness of material selected foruse in the lid also may be a factor in achieving the desired balance. Inone aspect, the lid may be made of a frangible plastic material such asfiberglass, polyethylene, rigid polyvinyl chloride, poly(methylmethacrylate), polypropylene, or polycarbonate, although other materialsmay be used, as would be appreciated by one of ordinary skill in theart. Additionally, it will be appreciated that the stronger the materialused, the thinner the lid may be made, and vice versa.

FIG. 71 illustrates how the stiffening members 762 rest on the aggregatelayer 752 and space the underside 760 of the lid 750 away from an upperend 766 of the aggregate 752, leading to formation of one or more voids768 between the aggregate 752 and the underside 760. Rather than restingdirectly on the aggregate, however, the EMAS may include one or moresupport sheets or a plurality of support props to receive a distal end.For example, FIG. 72 depicts the use of a plastic support sheet 772, andFIG. 73 depicts the use of a plurality of support props 774 disposedbetween the distal end 770 of the stiffening members 762 and an upperend 766 of the aggregate 752. Both the support sheet 772 and the supportprops 774 increase a surface contact area as compared to the distal end770 of the stiffening members 762, thereby reducing the pressure causedby a force on the lid 750 and distributing that force over a largerarea. Additionally, the support sheet 772 may be used in installationswhere greater confinement of the aggregate 752 is desired during anoverrun event, at it may inhibit upward movement of the aggregate 752into the void 768 during an overrun event.

FIGS. 74-77 depict various examples of support props 774. In particular,those props may be divided into two general categories, i.e., a firstcategory of point-type supports such as those in FIGS. 74 and 75, and asecond category of generally continuous supports, such as those in FIGS.76 and 77. Point supports may receive smaller segments of the stiffeningmembers but may provide an installer with greater freedom in positioningthe supports along the stiffening members. Conversely, the generallycontinuous supports may take up more room than the point supports, butthey also may provide a significant increase in surface area as comparedto the point supports, dramatically reducing the presence of stressconcentrations at the stiffening member-aggregate interface.

Turning to FIG. 78, one or more point anchors 776 similar to the pointanchors 60 described above then may be used to secure each lid 750 tothe underlying pavement 756. Each point anchor 776 may slidingly orthreadingly engage a rod 778 anchored into the pavement. An upper end780 of the rod further may include threading to receive one or morewashers or nuts in order to secure the point anchor 776 against the lid750. In particular, the point anchors 776 may include a fusible link(not shown) similar to the fusible link in the anchors 60 in order topromote fracturing of the link before fracturing of other components ofthe securement system, e.g., the upwardly extending rod or the pavementanchor.

While the foregoing written description of the invention enables one ofordinary skill to make and use what is considered presently to be thebest mode thereof, those of ordinary skill will understand andappreciate the existence of variations, combinations, and equivalents ofthe specific exemplary embodiment and method herein. The inventionshould therefore not be limited by the above described embodiment andmethod, but by all embodiments and methods within the scope and spiritof the invention as claimed.

We claim:
 1. A method of forming a vehicle arresting system, comprising:pouring a first aggregate layer on top of a substrate; compacting thefirst aggregate layer; installing a separation layer on top of the firstaggregate layer; pouring a second aggregate layer on top of theseparation layer; compacting the second aggregate layer; and installinga slab layer on top of the second aggregate layer.
 2. The method ofclaim 1, wherein either compacting step is performed by a bobcat orvibrator plate.
 3. The method of claim 1, wherein the first and secondaggregate layers are comprised of the same material.
 4. The method ofclaim 1, wherein the first and second aggregate layers are comprised ofdifferent materials.
 5. The method of claim 1, wherein the first andsecond aggregate layers are poured to approximately equal depths.
 6. Themethod of claim 1, wherein the first and second aggregate layers arepoured to different depths.
 7. The method of claim 1, wherein at leastone of the first and second aggregate layers comprises glass foam. 8.The method of claim 1, wherein the separation layer is a first slablayer.
 9. The method of claim 8, wherein the first slab layer ispre-cast.
 10. The method of claim 8, wherein the first slab iscast-in-place.
 11. The method of claim 1, wherein the separation layeris one of fiberglass, fiber cement board, or rigid polypropylene. 12.The method of claim 11, wherein the separation layer has a thicknessbetween about 1 mm and about 13 mm.
 13. The method of claim 1, whereinat least one of the separation layer and the slab layer comprises acementitious material having an oven-dry density of 100 lb/ft³ or less.14. The method of claim 13, wherein the cementitious material includesstable gas cells distributed throughout the material at a volumepercentage of 33% or greater by volume of the material.
 15. The methodof claim 13 wherein the cementitious material has a compressive strengthof 200 to 600 psi.
 16. A method of forming a vehicle arresting system,comprising: pouring a first aggregate layer on top of a substrate;compacting the first aggregate layer; installing a first slab layer ontop of the first aggregate layer; pouring a second aggregate layer ontop of the first slab layer; compacting the second aggregate layer; andinstalling a second slab layer on top of the second aggregate layer,wherein at least one of the first slab layer and the second slab layercomprises a cementitious material having an oven-dry density of 100lb/ft³ or less.
 17. The method of claim 16, wherein the cementitiousmaterial includes stable gas cells distributed throughout the materialat a volume percentage of 33% or greater by volume of the material. 18.The method of claim 16, wherein the cementitious material has acompressive strength of 200 to 600 psi.
 19. A method of forming avehicle arresting system, comprising: pouring a first aggregate layer ontop of a substrate; compacting the first aggregate layer; pouring asecond aggregate layer on top of the first aggregate layer; compactingthe second aggregate layer; pouring a third aggregate layer on top ofthe second aggregate layer; compacting the third aggregate layer; andinstalling a slab layer on top of the third aggregate layer.
 20. Themethod of claim 19, further comprising: installing a separation layerbetween at least one of the first and second aggregate layers and thesecond and third aggregate layers.
 21. The method of claim 19, whereinthe first, second, and third aggregate layers have substantially thesame depth.
 22. The method of claim 19, wherein at least one of thefirst, second, and third aggregate layers has a different depth thanothers of the first, second, and third aggregate layers.
 23. The methodof claim 19, wherein the first, second, and third aggregate layers allhave different depths.
 24. The method of claim 19, wherein at least oneof the first, second, and third aggregate layers comprises glass foam.25. The method of claim 19, wherein at least one of the first, second,and third aggregate layers comprises a different type of aggregate thanothers of the first, second, and third aggregate layers.
 26. The methodof claim 25, wherein the different type of aggregate is a differentgrade of glass foam as compared to a glass foam comprising at least oneof the others of the first, second, and third aggregate layers.
 27. Themethod of claim 19, wherein the slab layer comprises a cementitiousmaterial having an oven-dry density of 100 lb/ft³ or less.
 28. Themethod of claim 27 wherein the cementitious material includes stable gascells distributed throughout the material at a volume percentage of 33%or greater by volume of the material.
 29. The method of claim 27 whereinthe cementitious material has a compressive strength of 200 to 600 psi.